1. Field of the Invention
This invention relates generally to systems that indicate the exposure status of photographic film and, more particularly, to camera and film cassette systems that cooperate to visually indicate the exposure status of the film cassette.
2. Description of the Related Art
Photographic cameras typically accept roll strips of photographic film that are exposed one frame at a time. Many cameras are designed to accept rolls of film that are enclosed within a light-tight film container such as a cassette or a canister. A typical container is the familiar 35 mm format film. After the film container is received within the camera, the film is pulled out of the container and stretched across an exposure gate, where frames are exposed in sequence, one after the other. It can be desirable to interrupt the sequential exposure of frames of the film in mid-roll so that a camera user can rewind a partially exposed roll of film back into the light-tight container, remove the container from the camera, and temporarily store the container. At a later time, the camera user can reload the interrupted container back into the camera and then position the film at approximately the next unexposed frame location, ready to resume picture taking.
The mid-roll interrupt (MRI) operation has many advantages, primarily where a roll of film will not be completely exposed before it is desirable to load a new roll of film. For example, by removing a film strip in mid-roll, it is possible to maintain the same subject matter for an entire roll of exposures taken over time without discarding unexposed frames as the camera user changes to a new roll and a new photographic subject. The MRI feature also permits changing among different film types during a continuous picture taking session without discarding large portions of unexposed film, such as might be desirable under changing light conditions.
Some cameras provide an automatic mid-roll interrupt (MRI) function in which a partially exposed roll of film is automatically rewound into the film container when the MRI function is invoked and is automatically positioned at the next unexposed frame location upon being reloaded into the camera. Film cassettes designed for use with automatic MRI-capable cameras often include relatively complex mechanisms to ensure the cassette remains light-tight, and often include a film parking mechanism that prevents the roll strip of film from unravelling or unspooling within the cassette. Any unspooling of the film would make it very difficult to resume making exposures at the correct frame position. Film parking mechanisms can be relatively complex, having mechanisms for locking the spool and for positioning light-tight film cassette doors, and can require complex camera-cassette mechanical interfaces.
One problem that can be encountered with mid-roll interrupt operations is that an already-exposed roll of film can be inadvertently loaded and exposed once again, creating double images and mining the film. Therefore, film cassettes intended for use in conjunction with mid-roll interrupt operation also typically include a visual indication of the film status. In this way, a user is immediately informed of the film cassette status and does not attempt to load a cassette containing film that was already exposed or processed. Typically, the visual indication provided by such cassettes distinguishes the film status as being either unexposed, partially exposed, fully exposed, or processed.
As noted above, the mechanical interfaces between an MRI-capable camera and a film cassette can be relatively complex and costly. Both the mechanical interface and the film cassette design can be even more complex and costly if operation with both MRI and non-MRI cameras is to be supported and the visual exposure indication is to be provided. For example, if a film cassette is to be compatible with non-MRI cameras, then the camera-film cassette combination must automatically omit any visual indication of the film being partially exposed, as that would be a non-operational mode.
From the discussion above, it should be apparent that there is a need for a photographic camera and film cassette combination that provides the convenience and flexibility of the MRI feature and also provides dual operation such that MRI and non-MRI cameras can be operated with MRI and non-MRI film cassettes, without the complexity and cost associated with conventional camera-cassette combinations. The present invention fulfills this need.